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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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27 records · Page 2

Electronic Structure Theories of Singlet Fission and Multiple Exciton Generation (Final Report)

This DOE grant supported the development of electronic structure theory, algorithms, and computer programs for simulating singlet fission and multiple excision generation processes from Sept. 2013 to Aug. 2018 (which was terminated due to the PI’s departure from Northwestern University to industry). One of the main achievements is the development of the so-called active space decomposition (ASD) method hat describes exciton dynamics in organic semiconductors and spin dynamics in strongly correlated materials. The resulting software was interfaced with the Brilliantly Advanced General Electronic-structure Library (BAGEL) package and widely disseminated to the research community.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Listen: Oppenheimer’s office chair one of the only possessions the lab has from our first director

Even the father of the atomic bomb had to sit down somewhere. It's hard to believe that our legendary first Lab director and brilliant physicist J. Robert Oppenheimer did something as ordinary as using a chair at work like the rest of us do. However, aside from a recently gifted book, this chair from the 1940s is the only Oppenheimer possession that the Lab has. And Oppie fans love it. The chair is routinely loaned to museums nationwide for display.

99 GENERAL AND MISCELLANEOUS↗

A Birthday Tribute to Oppie. Listen to a rare interview from 1965, print a keepsake poster

The Lab’s first Director and brilliant physicist shied away from the spotlight, particularly after leaving Los Alamos following the end of World War II in 1945. But when J. Robert Oppenheimer spoke, his words commanded attention. In commemoration of what would’ve been Oppenheimer’s 117th birthday on April 22, the National Security Research Center (NSRC), the lab’s classified library, is sharing a rare interview from the Voices of the Manhattan Project and an original poster that can be printed and displayed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

w19_nubhlight (Final Report)

The in-spiral and merger of two neutron stars produces several signals observable on Earth. The in-spiral of two compact objects produces gravitational waves - ripples in spacetime - detectable by the LIGO and VIRGO detectors. The two stars will tidally disrupt each other, throwing off material, some of which escapes and some of which forms a disk of hot nuclear matter accreting onto the central remnant. This accretion drives a pair of powerful ultra-relativistic jets of material along the polar axis. These jets are ultimately responsible for producing short gamma-ray bursts, some of the most brilliant and energetic events in the cosmos.

79 ASTRONOMY AND ASTROPHYSICS↗

An April Fools’ Day read from Lab history Famed physicist Richard Feynman’s safecracking, cipher-creating sense of play

Richard Feynman was fresh out of Princeton University’s doctoral program when recruited to assist in the creation of the atomic bomb at Los Alamos. In 1943, Lab director J. Robert Oppenheimer wrote that the 24-year-old was, “by all odds the most brilliant young physicist here, and everyone knows this.” Feynman attempted to live and examine life in a state of play and, as such, it’s only fitting to take a look back at the Nobel Prize winning scientist’s years at the wartime Lab as April Fools’ Day approaches.

99 GENERAL AND MISCELLANEOUS↗

In Search of Strategic Advantage: Understanding the Landscape of Technology Competition

In an era of seemingly ever-increasing global tensions, technology competition is often mentioned as a pathway for U.S. and allied success. The opening arguments are often very simple. “This is the most important struggle of the 21st century.” “We cannot afford to lose this competition.” “The United States must not fall behind in this race.” “We must be faster, more agile, more committed, more thoughtful than our competitors.” Competition around a particular technology is described as a once in a generational struggle with immense stakes. “This is a Sputnik moment” is a common analogy. The solutions proposed are fairly straightforward – more of everything. We should spend more money. We should build more widgets or more factories. We should innovate more. We should focus more. We should attract more talent. We should file more patents. We should produce more PhDs. If we do more of everything, we will have more technology than our opponents, they will see our technological advantage, they will not challenge us, and therefore we will win. If we fail to do these things, we will lose. To paraphrase Homer Simpson, in national security policy discussions technology competition has become the cause of, and solution to, all of life’s problems. And yet, beyond doing more across the board technology competition is not at all simple. First, it is a concept increasingly muddled together with other big issues such as innovation policy, national defense strategy, great power competition, allied cooperation, public-private partnerships, and a host of other issues. Certain policies, systems, coalitions, and so on may be excellent for tackling one challenge, but far less optional for others. Second, it is inherently dynamic, an action-reaction cycle between multiple players. A brilliant opening move can be squandered or successfully countered in subsequent moves. Third, there are limits to what you can do - limited time, limited financial resources, limited human capital, and limited knowledge of what lies ahead. One is forced to choose.

99 GENERAL AND MISCELLANEOUS↗

Convolutional Neural Network for Segmenting Micro-X-ray Computed Tomography Images of Wood Cellular Structures

To further enhance the performance of wood products, improved tools are needed to study in situ cellular scale phenomena like mechanical deformations and moisture swelling. Micro-X-ray computed tomography (μXCT) using brilliant synchrotron light sources now has the spatial and temporal resolution for real-time visualization of phenomena in three-dimensional cellular structures. However, the tradeoff for speed includes the loss of intensity contrast between different types of materials within the imaged structure, such as cell wall and air in wood. This loss of contrast prevents traditional histogram-based segmentation methods from being used effectively. A new convolutional neural network (CNN) approach was therefore developed to segment fast μXCT images of wood into cell wall and air volumes. The fast μXCT and segmentation were demonstrated in the study of moisture swelling in loblolly pine (Pinus taeda) earlywood and latewood cellular structures conditioned at 0%, 33%, 75%, and 95% relative humidity (RH). The CNN segmentation results had a mean intersection over union (IoU) metric accuracy of 96%. Initial analysis of the swelling in the latewood revealed cell walls swelled about 25% when conditioned from 0% to 95% RH. Additionally, the widths of ray cell lumina in the transverse plane of latewood could be observed to increase at higher RH. The segmentation method presented here will facilitate future quantitative analyses in in situ μXCT studies of wood and other similar cellular materials.

Arzola-Villegas, Xavier (ORCID:0000000305369766)↗

A Platform for Ultra-Fast Proton Probing of Matter in Extreme Conditions

Recent developments in ultrashort and intense laser systems have enabled the generation of short and brilliant proton sources, which are valuable for studying plasmas under extreme conditions in high-energy-density physics. However, developing sensors for the energy selection, focusing, transport, and detection of these sources remains challenging. This work presents a novel and simple design for an isochronous magnetic selector capable of angular and energy selection of proton sources, significantly reducing temporal spread compared to the current state of the art. The isochronous selector separates the beam based on ion energy, making it a potential component in new energy spectrum sensors for ions. Analytical estimations and Monte Carlo simulations validate the proposed configuration. Due to its low temporal spread, this selector is also useful for studying extreme states of matter, such as proton stopping power in warm dense matter, where short plasma stagnation time (<100 ps) is a critical factor. The proposed selector can also be employed at higher proton energies, achieving final time spreads of a few picoseconds. This has important implications for sensing technologies in the study of coherent energy deposition in biology and medical physics.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Assessing Gender Bias in Particle Physics and Social Science Recommendations for Academic Jobs

We investigated gender bias in letters of recommendation as a possible cause of the under-representation of women in Experimental Particle Physics (EPP), where about 15% of faculty are female-well below the 60% level in psychology and sociology. We analyzed 2206 letters in EPP and these two social sciences using standard lexical measures as well as two new measures: author status and an open-ended search for gendered language. In contrast to former studies, women were not depicted as more communal, less agentic, or less standout. Lexical measures revealed few gender differences in either discipline. The open-ended analysis revealed disparities favoring women in social science and men in EPP. However, female EPP candidates were characterized as “brilliant” in nearly three times as many letters as were men.

99 GENERAL AND MISCELLANEOUS↗